Height control arrangement for a strike-off plate

ABSTRACT

A height control arrangement for a strike-off plate of an asphalt paver screed assembly is disclosed. The screed assembly has at least one main screed unit and at least one screed extension unit mounted in front of the main screed unit. The height control arrangement includes an actuator connected with the strike-off plate mounted in front of the main screed unit at a position ahead of the screed extension unit. A sensor measures the amount of material built up behind the strike off plate and sends an input signal to a controller responsive to the amount of material. The controller sends a control signal to the actuator to adjust the height of the strike off plate responsive to the magnitude of the input signal.

TECHNICAL FIELD

[0001] The present invention relates generally to asphalt paver screeds and more particularly to a height control arrangement for a strike-off plate for controlling the amount of asphalt material supplied to the main screed.

BACKGROUND ART

[0002] Asphalt paving machines have a hopper that receives hot asphalt paving material located at the front of the machine. A conveyor for delivers the paving material from the hopper to the rear of the machine and deposits the asphalt at the back of the paver onto the road surface being paved. An auger is located at the rear of the paver for distributing some of the asphalt material laterally to the sides of the road surface. The asphalt paver also includes a floating screed, which is pulled behind the auger, for smoothing out and compressing the asphalt to the desired road mat thickness. A pair of tow arms pulls the screed unit behind the auger. The tow arms have forward ends pivotally mounted to the sides of asphalt paver and rearward ends pivotally mounted to the screed.

[0003] Many modern screeds are provided with a pair of extendible screed units attached to a main screed unit. Each extendible screed unit is movable laterally to one side of the main screed unit in order to vary the width the road mat being laid by the paver. Some extendible screed units are mounted behind the main screed unit. However, front mounted extendible screed units have become popular due to certain advantages they afford over rear mounted extendible screed units. The front mounted screeds use a strike-off plate positioned in front of the extension units to limit the amount of paving material between the side extension units during retraction.

[0004] Screeds are provided with adjustments for controlling the “pitch” or “angle of attack” of the screed relative to the desired surface of the paving mat for controlling the depth of the mat being laid. For instance, raising the leading edge of the screed plate increases the angle of attack, thus increasing the depth of the mat being laid. However as the angle of attack is increased, the height of the strike-off plate of prior screeds also increased. Because such strike-off plate is mounted at a substantial distance ahead of the main screed in front of the screed extensions, the rise in height of the strike-off plate is disproportionately greater than the increase in the mat height being formed by the screed. This results in too much asphalt material being fed to the main screed and an undesirable build-up between the screed extensions. One prior design that addresses this problem is disclosed in U.S. Pat. No. 6,056,474 issued May 2, 2000 to David W. Nolan and is assigned to the owner of the present application.

DISCLOSURE OF THE INVENTION

[0005] The one aspect of the present invention a height control arrangement is provided for a strike-off plate of an asphalt paver screed assembly. The screed assembly has at least one main screed unit and at least one screed extension unit. The screed extension unit is mounted in front of the main screed unit and is laterally movable beyond one end of said main screed unit. The height control arrangement has the strike-off plate mounted in front of the main screed unit at a position ahead of the screed extension unit. An actuator is connected with the strike-off plate and a sensor is mounted behind the strike-off plate and in front of the main screed unit. The sensor is adapted for measuring an amount of material. A controller is connected to control the actuator responsive to the amount of material so as to adjust the height of the strike-off plate.

[0006] In yet another aspect of the present invention a method is provided for controlling the height of a strike off plate of an asphalt paver screed assembly. The screed assembly has at least one main screed unit and at least one screed extension unit mounted in front of said main screed unit. The method comprising the steps of sensing an amount of material built up behind said strike off plate and in front of said main screed unit and then adjusting the height of said strike off plate in responsive to the amount of material sensed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a diagrammatic top plan view of a screed assembly embodying a height control arrangement of the present invention;

[0008]FIG. 2 is a diagrammatic side cross-sectional view taken along line 2-2 of FIG. 1;

[0009]FIG. 3 is a diagrammatic side cross-sectional view similar to FIG. 2, but with the pitch angle of the screed assembly being adjusted upwardly; and

[0010]FIG. 4 is a simplified block diagram of a control system for the height control arrangement.

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] Referring now to FIG. 1 of the drawings, a top view of a floating screed assembly is diagrammatically illustrated at 10 for an asphalt paving machine (not shown). The screed assembly includes at least one main screed section 12. Preferably, as is customary in the art, the main screed section 12 includes a pair of main screed units 14,16 joined together about a centerline 18, which is oriented in the direction of travel and generally along the centerline of the paving machine. The main screed units 14,16 are joined together in a manner so as to be capable of being disposed at a slight angle with respect to each other for a crowning of the paved road surface about the centerline 18. The screed assembly is towed behind the asphalt paver by means of a pair of tow arms 20,22, each having a forward end thereof (not shown) pivotally connected to a respective side of the paving machine. Each tow arm 20,22 has a rearward end 24 having a drop arm portion 26, as best seen in FIG. 2.

[0012] The two main screed units 14,16 are, in general, mirror images of each other and only one will be further described and shown in the remaining drawings. As shown in FIG. 2, screed unit 14 includes a bottom sole plate 30, a generally vertical front plate 32 joining with the sole plate at a rounded lower front corner 34. The screed unit 14 also includes an outer side plate 36 and a tower plate 38 secured adjacent and extending above the outer side plate 36. The tow arm drop arm portion 26 extends adjacent the tower plate 38 and has a lower end 40 pivotally connected to the screed unit 14 by a pivot connection 42.

[0013] An adjustment mechanism 44 is provided for adjusting the pitch or attack angle of the screed assembly 10 slightly relative to a surface 46 being paved in order to control the depth of the mat. The adjustment mechanism 44 can be of any well-known type.

[0014] The screed assembly 10 also includes a pair of front mounted screed extensions 56,58, as shown in FIG. 1. Screed extensions are also, in general, mirror images of each other and only one will be further described and shown in the remaining drawings. Referring to FIG. 2, screed extension 56 includes a sole plate 60 and a front plate 62 joined by a rounded front corner 64. Each extension screed 56,58 is mounted to its respective main screed unit 14,16 and is selectively movable laterally from its extended position shown in FIG. 1 to a retracted position adjacent the centerline 18 in a known manner.

[0015] A pair of strike-off plates 66, 68 extend across the length of the main screed units 14,16 at a position ahead of the screed extensions 56,58. The pair of strike-off plates 66,68 have a bottom edge 70, a top edge 72 and inner and outer side edges 74,76. Each inner side edge 74 is disposed adjacent the centerline 18. Each strike-off plate 66,68 is provided with a length sufficient to have a respective one of its opposite outer side edges 76 overlap its respective screed extension 56,58 when such screed extension is in the extended position as shown in FIG. 1. Such outer side edges 76 are preferably angled toward the front plate 62 of its respective screed extension 56,58 for directing asphalt material toward the outer ends of the screed extensions.

[0016] Referring to FIGS. 2 and 3, a height adjustment arrangement 78 includes a support assembly 80 to mount the strike-off plates 66,68 in front of their respective main screed units 14,16 at a position ahead of the screed extensions 56,58. Support assembly 80 preferably includes separate components for each main screed unit 14,16. As each main screed unit 14,16 includes a separate height control arrangement 78 and are mirror images of one another, only one will be described herein.

[0017] In the embodiment shown, the support assembly 80 includes a pair of laterally spaced L-shaped brackets 86,88, each bracket having a horizontal leg 90 and a vertical leg 92. A distal rearward end 94 of each horizontal leg 90 is attached to the main screed unit 14, while a forward proximal end 96 is disposed toward a respective one of the inner and outer side edges 74,76 of strike-off plate 66. The vertical leg 92 extends downwardly from the forward proximal end 96 of the horizontal leg 90 and is disposed in a gap 98 between the screed extension 56 and strike-off plate 66.

[0018] The support assembly 80 includes a linkage mechanism 100 that is pivotally supported by the same. In particular, the linkage mechanism 100 includes a bellcrank 102 having a first distal end 104 and a second distal end 106. An actuator 108 has a first end 110 pivotally connected to the first distal end 104 and a second end 112 pivotally connected to the tow arm 20. Actuator 108 is shown as being a fluid cylinder however it should be understood that any suitable actuator, such as a ball screw, motor with a rack and pinion arrangement or the like can also be used. A first connecting rod 114 having one end 116 pivotally connected to the second distal end 106 of the bellcrank 102 and its other end 118 connected to the strike-off plate 66. A pivot bar 120 is rotatably mounted to the forward proximal ends 96 of the horizontal legs 90 of each L-shaped bracket 86,88. A lever 122 (FIG. 1) is carried on the pivot bar 120 and is connected to the strike-off plate 66 by a second connecting rod 124 in a similar manner. Lever 122 is disposed adjacent the inner side edge 74 of the strike-off plate 66.

[0019] As seen in FIG. 1, a sensor 130 is mounted from each L-shaped bracket 88 behind the strike-off plates 86,88 and in front of the main screed units 14,16 and between the screed extensions 56,58. Sensor 130 can be known vision sensors such as micro pulse radar, ultrasonic sensor, proximity sensors, optical or can be contact type sensors such as limit switches, pressure sensors and the like. Sensor 130 is positioned to measure an amount of a material 138 such as hot mix asphalt behind the strike-off plates 66,68.

[0020] Referring now to FIG. 4 a simplified block diagram of a control system 140 for the height control arrangement 78 is shown. The sensor 130 is connected to a controller 142 as by electric conductor or by radio frequency. The controller 142 includes stored data 144 that is representative to the desired position of the bottom edge 70 of the strike-off plate 66 for a given angle of attack of sole plate 30 of the main screed 14 and thickness of mat to be laid. Controller 142 is in turn connected to a hydraulic system 146, which is in turn connected to the actuator 108. It should be noted however that the controller 142 could be directly connected to the actuator 108.

INDUSTRIAL APPLICABILITY

[0021] In operation, the construction of the height control arrangement 78 of the present invention is effective in automatically adjusting the height of strike-off plates 66,68. During operation the sensors 130 continuously measuring the amount of material 132 after the strike-off plates 66,68 and in front of each of the main screed units 14,16. The sensors 130 send signals to the controller 142 responsive to the amount of material 132 measured. The controller 142 compares these signals to the stored data 144. The controller 142 then generates and sends a control signal to the hydraulic system 146 to actuate the actuator 108. The control signal raises or lowers the strike off plates 66,68 based on the desired mat thickness being laid and the attack angle of the screeds 14,16. For example, if the amount of material 132 measured is greater than desired for a given mat thickness the controller 142 sends a signal to the actuator 138 to lower the strike-off plates 66,68. Conversely, if the amount of material 138 measured is less than desired for a given mat thickness the controller 142 sends a signal to the actuator 138 to raise the strike-off plates 66,68.

[0022] Additionally it should be noted, the linkage mechanism 100 is adjustable in length. By making the linkage mechanism 100 adjustable, the height of the bottom edges 70 of the strike-off plates 66,68 relative the screeds may be adjusted to a desired height to let either more or less asphalt material pass under the strike-off plates 66,68.

[0023] The primary advantage of the strike-off plate height control arrangement 78, though, is to automatically control the amount of material 138 getting to the main screed units 14,16 between the screed extensions 56,58. 

1. A height control arrangement for a strike-off plate of an asphalt paver screed assembly, said screed assembly having at least one main screed unit and at least one screed extension unit mounted in front of said main screed unit and being laterally movable beyond one end of said main screed unit, said height control arrangement comprising: said strike-off plate being mounted in front of the main screed unit at a position ahead of the screed extension unit; an actuator connected with said strike-off plate; a sensor mounted behind said strike-off plate and in front of the main screed unit and adapted for measuring an amount of material; and a controller connected to control the actuator responsive to the amount of material so as to adjust the height of said strike-off plate.
 2. The height control arrangement of claim 1 wherein said sensor measures the amount of material by vision.
 3. The height control arrangement of claim 1 wherein said sensor measures the amount of material by contact.
 4. The height control arrangement of claim 1 includes a linkage mechanism pivotally supported by a support arm mechanism, said linkage mechanism having a first distal end being pivotally connected to said actuator and a second distal end connected to said strike-off plate.
 5. The height control arrangement of claim 4 wherein said linkage mechanism is length adjustable.
 6. A method for controlling the height of a strike off plate of an asphalt paver screed assembly, said screed assembly having at least one main screed unit and at least one screed extension unit mounted in front of said main screed unit comprising the steps of: sensing an amount of material built up behind said strike off plate and in front of said main screed unit; and adjusting the height of said strike off plate in responsive to the amount of material sensed.
 7. The method of claim 6 wherein the step of sensing includes the step of sending a signal responsive to the amount of material sensed to a controller.
 8. The method of claim 7 including the step of comparing the signal responsive to the amount of material sensed to stored data.
 9. The method of claim 6 including the step of actuating an actuator to adjust the height of said strike off plate. 